The focus of this proposal is to determine the microbial etiology of initial periodontitis in adults. The potential of microbial diagnosis to identify subjects at risk of disease, and the stability of the subgingival microbial over time, will also be evaluated. Identification of initial periodontitis pathogens will be allow other research studies, and patient prevention and therapy, to be targeted to the species associated with the infection. The specific aims explore the associations between recognized microbial risk markers- putative pathogens- particularly those associated with initial periodontal disease, with early signs of disease, and with progressing sites. The aims also seek new microbial risk markers, including recognized and new species of spirochetes, by studying a large diverse population. Microorganisms in 300 subjects (100 subjects at Boston University Dental School Site) will be examined using new molecular biology techniques for rapid species assay of subgingival and tongue samples. The tongue would provide a convenient sample for microbial diagnosis of initial periodontitis. Information from this study will significantly advance understanding of the microbial etiology of initial periodontitis. This information will have a profound significance for basic studies in periodontal research, and in microbial identification of subjects at risk for periodontitis for clinical and epemiological studies.